The present invention relates to a seat belt device that is provided on a vehicle, for example, an automobile, for the purpose of protecting an occupant. More particularly, the present invention relates to a seat belt retractor locking the reel shaft from rotating to prevent the webbing from being pulled out when an emergency situation occurs.
Conventional seat belt retractors are provided on automobiles and other vehicles. One of the conventional seat belt retractors has a reel shaft for winding up a webbing and prevents the reel shaft from rotating in an unwinding direction by a frame thereof when it is desired. The seat belt retractor is a frame locking type as disclosed in Japenese Published Unexamined Patent Application No. H5 (1993)-193441.
FIG. 19 is a sectional view of the seat belt retractor. FIG. 20 is a sectional view taken along a line XX--XX of FIG. 19. In these figures, the numeral 101 is a seat belt retractor, the numeral 102 is a U-shaped frame, the numeral 102a is a left-hand side wall, the numeral 102b is a right-hand side wall, the numeral 102c is teeth, the numeral 103 is a reel shaft, the numeral 104 is a webbing, the numeral 105 is a lock gear, the numeral 105a is external teeth, the numerals 105b, 105c are cam holes, the numeral 106 is a main pawl, the numeral 107 is a backup pawl, the numeral 108 is a joint pin, the numeral 109 is an inertia member, the numeral 109a is a pawl, the numeral 110 is a cover, the numeral 110a is inner teeth, the numeral 111 is deceleration sensing means, the numeral 111a is an inertia ball, the numeral 111b is a lever, the numeral 111c is a pawl, and the numeral 112 is biasing force application means.
When a predetermined degree of deceleration acts on the vehicle, an inertia ball 111a moves and lever 111b pivots to the position as shown by the two-dot chin line. Since the webbing 104 is unwound due to the deceleration, the reel shaft 103 and lock gear 105 thereby rotate in a webbing unwinding direction .alpha.. The external teeth 105a engage with the pawl 111c of the lever 111b to stop the lock gear 105 so that only the reel shaft 103 rotates. The main pawl 106 moves along the cam hole 103b, then engages with the teeth 102c of the left-hand side wall 102a. At the same time, the joint pin 108 rotates along the cam hole 105c so that the backup pawl 107 rotates to engage with the teeth 102d of the right-hand side wall 102b. Thereby, the reel shaft 103 stops rotating and the webbing 104 is prevented from being unwound.
On the other hand, as the webbing 104 is unwound rapidly, the reel shaft 103 and the lock gear 105 rapidly rotate in the webbing unwinding direction a, while the inertia member 109 is positioned as shown by the two-dot chain line because of the inertia delay. In this state, the reel shaft 103 and the lock gear 105 rotate in the direction .alpha. so that the pawl 109a of the inertia member 109 engages with the teeth 110a. The lock gear 105 then stops and only the reel shaft 103 rotates. Therefore, the main pawl 106 engages with the teeth 102c, the backup pawl 107 engages with the teeth 102d and the reel shaft 103 stops rotating so that the webbing 104 is prevented from being unwound as described above.
In the conventional seat belt retractor 101, the number of the teeth 102c, 102d formed on the frame 102 is relatively great and the number of the inner teeth 110a of the cover 110 is the same so as to restrain the amount of the webbing 104 in the unwound direction as little as possible during the deceleration or when the webbing 104 is unwound rapidly.
However, in the conventional seat belt retractor, when the webbing 104 is unwound to the end against the biasing force of the biasing force application means 112, the inertia member 109 pivots to the position as shown by the two-dot chain line by its inertia so as to engage with the teeth 110a. This tends to occur the problem known as an "end lock", that is, to prevent the webbing from being wound.